Lustre or luster is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux, meaning "light", implies radiance, gloss, or brilliance. A range of terms are used to describe lustre, such as earthy, metallic and silky; the term vitreous refers to a glassy lustre. A list of these terms is given below. Lustre varies over a wide continuum, so there are no rigid boundaries between the different types of lustre; the terms are combined to describe intermediate types of lustre. Some minerals exhibit unusual optical phenomena, such as asterism or chatoyancy. A list of such phenomena is given below. Adamantine minerals possess a superlative lustre, most notably seen in diamond; such minerals are transparent or translucent, have a high refractive index. Minerals with a true adamantine lustre are uncommon, with examples being cerussite and cubic zirconia. Minerals with a lesser degree of lustre are referred to as subadamantine, with some examples being garnet and corundum.
Dull minerals exhibit little to no lustre, due to coarse granulations which scatter light in all directions, approximating a Lambertian reflector. An example is kaolinite. A distinction is sometimes drawn between dull minerals and earthy minerals, with the latter being coarser, having less lustre. Greasy minerals resemble grease. A greasy lustre occurs in minerals containing a great abundance of microscopic inclusions, with examples including opal and cordierite, jadeite. Many minerals with a greasy lustre feel greasy to the touch. Metallic minerals have the lustre of polished metal, with ideal surfaces will work as a reflective surface. Examples include galena and magnetite. Pearly minerals consist of thin transparent co-planar sheets. Light reflecting from these layers give them a lustre reminiscent of pearls; such minerals possess perfect cleavage, with examples including stilbite. Resinous minerals have the appearance of chewing gum or plastic. A principal example is amber, a form of fossilized resin.
Silky minerals have a parallel arrangement of fine fibres, giving them a lustre reminiscent of silk. Examples include asbestos and the satin spar variety of gypsum. A fibrous lustre has a coarser texture. Submetallic minerals are duller and less reflective. A submetallic lustre occurs in near-opaque minerals with high refractive indices, such as sphalerite and cuprite. Vitreous minerals have the lustre of glass; this type of lustre is one of the most seen, occurs in transparent or translucent minerals with low refractive indices. Common examples include calcite, topaz, beryl and fluorite, among others. Waxy minerals have a lustre resembling wax. Examples include chalcedony. Asterism is the display of a star-shaped luminous area, it is seen in some rubies, where it is caused by impurities of rutile. It can occur in garnet and spinel. Aventurescence is a reflectance effect like that of glitter, it arises from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they influence the material's body colour.
In aventurine quartz, chrome-bearing fuchsite makes for a green stone and various iron oxides make for a red stone. Chatoyant minerals display luminous bands; such minerals are composed of parallel fibers, which reflect light into a direction perpendicular to their orientation, thus forming narrow bands of light. The most famous examples are tiger's eye and cymophane, but the effect may occur in other minerals such as aquamarine and tourmaline. Color change is most found in alexandrite, a variety of chrysoberyl gemstones. Other gems occur in color-change varieties, including sapphire, spinel. Alexandrite displays a color change dependent upon light, along with strong pleochroism; the gem results from small-scale replacement of aluminium by chromium oxide, responsible for alexandrite's characteristic green to red color change. Alexandrite from the Ural Mountains in Russia is green by red by incandescent light. Other varieties of alexandrite may be yellowish or pink in daylight and a columbine or raspberry red by incandescent light.
The optimum or "ideal" color change would be fine emerald green to fine purplish red, but this is rare. Iridescence is the'play' or'fire' of rainbow-coloured light caused by thin regular structures or layers beneath the surface of a gemstone. Similar to a thin film of oil on water, these layers interfere with the rays of reflected light, reinforcing some colours and cancelling others. Iridescence is seen at its best in precious opal. Schiller, from German for "color play", is the metallic iridescence originating from below the surface of a stone that occurs when light is reflected between layers of minerals, it is seen in moonstone and labradorite and is similar to adularescence and aventurescence
Encyclopædia Britannica, Eleventh Edition
The Encyclopædia Britannica, Eleventh Edition is a 29-volume reference work, an edition of the Encyclopædia Britannica. It was developed during the encyclopaedia's transition from a British to an American publication; some of its articles were written by the best-known scholars of the time. This edition of the encyclopedia, containing 40,000 entries, is now in the public domain, many of its articles have been used as a basis for articles in Wikipedia. However, the outdated nature of some of its content makes its use as a source for modern scholarship problematic; some articles have special value and interest to modern scholars as cultural artifacts of the 19th and early 20th centuries. The 1911 eleventh edition was assembled with the management of American publisher Horace Everett Hooper. Hugh Chisholm, who had edited the previous edition, was appointed editor in chief, with Walter Alison Phillips as his principal assistant editor. Hooper bought the rights to the 25-volume 9th edition and persuaded the British newspaper The Times to issue its reprint, with eleven additional volumes as the tenth edition, published in 1902.
Hooper's association with The Times ceased in 1909, he negotiated with the Cambridge University Press to publish the 29-volume eleventh edition. Though it is perceived as a quintessentially British work, the eleventh edition had substantial American influences, not only in the increased amount of American and Canadian content, but in the efforts made to make it more popular. American marketing methods assisted sales; some 14% of the contributors were from North America, a New York office was established to coordinate their work. The initials of the encyclopedia's contributors appear at the end of selected articles or at the end of a section in the case of longer articles, such as that on China, a key is given in each volume to these initials; some articles were written by the best-known scholars of the time, such as Edmund Gosse, J. B. Bury, Algernon Charles Swinburne, John Muir, Peter Kropotkin, T. H. Huxley, James Hopwood Jeans and William Michael Rossetti. Among the lesser-known contributors were some who would become distinguished, such as Ernest Rutherford and Bertrand Russell.
Many articles were carried over from some with minimal updating. Some of the book-length articles were divided into smaller parts for easier reference, yet others much abridged; the best-known authors contributed only a single article or part of an article. Most of the work was done by British Museum scholars and other scholars; the 1911 edition was the first edition of the encyclopædia to include more than just a handful of female contributors, with 34 women contributing articles to the edition. The eleventh edition introduced a number of changes of the format of the Britannica, it was the first to be published complete, instead of the previous method of volumes being released as they were ready. The print type was subject to continual updating until publication, it was the first edition of Britannica to be issued with a comprehensive index volume in, added a categorical index, where like topics were listed. It was the first not to include long treatise-length articles. Though the overall length of the work was about the same as that of its predecessor, the number of articles had increased from 17,000 to 40,000.
It was the first edition of Britannica to include biographies of living people. Sixteen maps of the famous 9th edition of Stielers Handatlas were translated to English, converted to Imperial units, printed in Gotha, Germany by Justus Perthes and became part this edition. Editions only included Perthes' great maps as low quality reproductions. According to Coleman and Simmons, the content of the encyclopedia was distributed as follows: Hooper sold the rights to Sears Roebuck of Chicago in 1920, completing the Britannica's transition to becoming a American publication. In 1922, an additional three volumes, were published, covering the events of the intervening years, including World War I. These, together with a reprint of the eleventh edition, formed the twelfth edition of the work. A similar thirteenth edition, consisting of three volumes plus a reprint of the twelfth edition, was published in 1926, so the twelfth and thirteenth editions were related to the eleventh edition and shared much of the same content.
However, it became apparent that a more thorough update of the work was required. The fourteenth edition, published in 1929, was revised, with much text eliminated or abridged to make room for new topics; the eleventh edition was the basis of every version of the Encyclopædia Britannica until the new fifteenth edition was published in 1974, using modern information presentation. The eleventh edition's articles are still of value and interest to modern readers and scholars as a cultural artifact: the British Empire was at its maximum, imperialism was unchallenged, much of the world was still ruled by monarchs, the tragedy of the modern world wars was still in the future, they are an invaluable resource for topics omitted from modern encyclopedias for biography and the history of science and technology. As a literary text, the encyclopedia has value as an example of early 20th-century prose. For example, it employs literary devices, such as pathetic fallacy, which are not as common in modern reference texts.
In 1917, using the pseudonym of S. S. Van Dine, the US art critic and author Willard Huntington Wright published Misinforming a Nation, a 200+
Bismuth is a chemical element with symbol Bi and atomic number 83. It is a pentavalent post-transition metal and one of the pnictogens with chemical properties resembling its lighter homologs arsenic and antimony. Elemental bismuth may occur although its sulfide and oxide form important commercial ores; the free element is 86% as dense as lead. It is a brittle metal with a silvery white color when freshly produced, but surface oxidation can give it a pink tinge. Bismuth is the most diamagnetic element, has one of the lowest values of thermal conductivity among metals. Bismuth was long considered the element with the highest atomic mass, stable, but in 2003 it was discovered to be weakly radioactive: its only primordial isotope, bismuth-209, decays via alpha decay with a half-life more than a billion times the estimated age of the universe; because of its tremendously long half-life, bismuth may still be considered stable for all purposes. Bismuth metal has been known since ancient times, although it was confused with lead and tin, which share some physical properties.
The etymology is uncertain, but comes from Arabic bi ismid, meaning having the properties of antimony or the German words weiße Masse or Wismuth, translated in the mid-sixteenth century to New Latin bisemutum. Bismuth compounds account for about half the production of bismuth, they are used in cosmetics, a few pharmaceuticals, notably bismuth subsalicylate, used to treat diarrhea. Bismuth's unusual propensity to expand as it solidifies is responsible for some of its uses, such as in casting of printing type. Bismuth has unusually low toxicity for a heavy metal; as the toxicity of lead has become more apparent in recent years, there is an increasing use of bismuth alloys as a replacement for lead. The name bismuth dates from around the 1660s, is of uncertain etymology, it is one of the first 10 metals to have been discovered. Bismuth appears in the 1660s, from obsolete German Bismuth, Wissmuth; the New Latin bisemutum is from the German Wismuth from weiße Masse, "white mass". The element was confused in early times with tin and lead because of its resemblance to those elements.
Bismuth has been known since ancient times, so no one person is credited with its discovery. Agricola, in De Natura Fossilium states that bismuth is a distinct metal in a family of metals including tin and lead; this was based on observation of their physical properties. Miners in the age of alchemy gave bismuth the name tectum argenti, or "silver being made," in the sense of silver still in the process of being formed within the Earth. Beginning with Johann Heinrich Pott in 1738, Carl Wilhelm Scheele and Torbern Olof Bergman, the distinctness of lead and bismuth became clear, Claude François Geoffroy demonstrated in 1753 that this metal is distinct from lead and tin. Bismuth was known to the Incas and used in a special bronze alloy for knives. Bismuth is a brittle metal with a white, silver-pink hue with an iridescent oxide tarnish showing many colors from yellow to blue; the spiral, stair-stepped structure of bismuth crystals is the result of a higher growth rate around the outside edges than on the inside edges.
The variations in the thickness of the oxide layer that forms on the surface of the crystal cause different wavelengths of light to interfere upon reflection, thus displaying a rainbow of colors. When burned in oxygen, bismuth burns with a blue flame and its oxide forms yellow fumes, its toxicity is much lower than that of its neighbors in the periodic table, such as lead and polonium. No other metal is verified to be more diamagnetic than bismuth. Of any metal, it has one of the lowest values of thermal conductivity and the highest Hall coefficient, it has a high electrical resistivity. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, despite being a post-transition metal. Elemental bismuth is denser in the liquid phase than the solid, a characteristic it shares with germanium, silicon and water. Bismuth expands 3.32% on solidification. Though unseen in nature, high-purity bismuth can form distinctive, colorful hopper crystals, it is nontoxic and has a low melting point just above 271 °C, so crystals may be grown using a household stove, although the resulting crystals will tend to be lower quality than lab-grown crystals.
At ambient conditions bismuth shares the same layered structure as the metallic forms of arsenic and antimony, crystallizing in the rhombohedral lattice, classed into trigonal or hexagonal crystal systems. When compressed at room temperature, this Bi-I structure changes first to the monoclinic Bi-II at 2.55 GPa to the tetragonal Bi-III at 2.7 GPa, to the body-centered cubic Bi-IV at 7.7 GPa. The corresponding transitions can be monitored via changes in electrical conductivity. Bismuth is stable to both moist air at ordinary temperatures; when red-hot, it reacts with water to make bismuth oxide. 2 Bi + 3 H2O → Bi2O3 + 3 H2It reacts with fluorine to
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations; the surface along which the lattice points are shared in twinned crystals is called a composition surface or twin plane. Crystallographers classify twinned crystals by a number of twin laws; these twin laws are specific to the crystal system. The type of twinning can be a diagnostic tool in mineral identification. Twinning is an important mechanism for permanent shape changes in a crystal. Twinning can be a problem in X-ray crystallography, as a twinned crystal does not produce a simple diffraction pattern. Twin laws are either defined by the direction of the twin axes. If the twin law can be defined by a simple planar composition surface, the twin plane is always parallel to a possible crystal face and never parallel to an existing plane of symmetry. If the twin law is a rotation axis, the composition surface will be irregular, the twin axis will be perpendicular to a lattice plane, but will never be an even-fold rotation axis of the existing symmetry.
For example twinning cannot occur on a new 2 fold axis, parallel to an existing 4-fold axis. In the isometric system, the most common types of twins are the Spinel Law, where the twin axis is perpendicular to an octahedral face, the Iron Cross, the interpenetration of two pyritohedrons a subtype of dodecahedron. In the hexagonal system, calcite shows the contact. Quartz shows the Brazil Law, Dauphiné Law which are penetration twins caused by transformation and Japanese Law, caused by accidents during growth. In the tetragonal system, cyclical contact twins are the most observed type of twin, such as in rutile titanium dioxide and cassiterite tin oxide. In the orthorhombic system, crystals twin on planes parallel to the prism face, where the most common is a twin which produces cyclical twins, such as in aragonite and cerussite. In the monoclinic system, twin occur most on the planes and by the Manebach Law, Carlsbad Law, Braveno Law in orthoclase, the Swallow Tail Twins in gypsum. In the triclinic system, the most twinned crystals are the feldspar minerals plagioclase and microcline.
These minerals show the Pericline Laws. Simple twinned crystals may be contact twins or penetration twins. Contact twins share a single composition surface appearing as mirror images across the boundary. Plagioclase, quartz and spinel exhibit contact twinning. Merohedral twinning occurs when the lattices of the contact twins superimpose in three dimensions, such as by relative rotation of one twin from the other. An example is metazeunerite. In penetration twins the individual crystals have the appearance of passing through each other in a symmetrical manner. Orthoclase, staurolite and fluorite show penetration twinning. If several twin crystal parts are aligned by the same twin law they are referred to as multiple or repeated twins. If these multiple twins are aligned in parallel they are called polysynthetic twins; when the multiple twins are not parallel they are cyclic twins. Albite and pyrite show polysynthetic twinning. Spaced polysynthetic twinning is observed as striations or fine parallel lines on the crystal face.
Rutile, aragonite and chrysoberyl exhibit cyclic twinning in a radiating pattern. But in general, based on the relationship between the twin axis and twin plane, there are 3 types of twinning: 1-parallel twinning, when the twin axis and compositional plane lie parallel to each other, 2-normal twining, when the twin plane and compositional plane lie and 3-complex twining, a combination of parallel twinning and normal twinning on one compositional plane. There are three modes of formation of twinned crystals. Growth twins are the result of an interruption or change in the lattice during formation or growth due to a possible deformation from a larger substituting ion. Annealing or transformation twins are the result of a change in crystal system during cooling as one form becomes unstable and the crystal structure must re-organize or transform into another more stable form. Deformation or gliding twins are the result of stress on the crystal. If a metal with face-centered cubic structure, like Al, Cu, Ag, Au, etc. is subjected to stress, it will experience twinning.
The formation and migration of twin boundaries is responsible for ductility and malleability of fcc metals. Deformation twinning is a common result of regional metamorphism. Crystal twinning is used as an indicator of force direction in mountain building processes in orogeny research. Crystals that grow adjacent to each other may be aligned to resemble twinning; this parallel growth reduces system energy and is not twinning. Twinning can occur by cooperative displacement of atoms along the face of the twin boundary; this displacement of a large quantity of atoms requires significant energy to perform. Therefore, the theoretical stress required to form a twin is quite high, it is believed that twinning is associated with dislocation motion on a coordinated scale, in contrast to slip, caused by independent glide at several locations in the crystal. Twinning and slip are competitive mechanisms for crystal deformation; each mechanism is dominant under certain conditions. In fcc metals, slip is always dominant because the stres
In mineralogy, crystal habit is the characteristic external shape of an individual crystal or crystal group. A single crystal's habit is a description of its general shape and its crystallographic forms, plus how well developed each form is. Recognizing the habit may help in identifying a mineral; when the faces are well-developed due to uncrowded growth a crystal is called euhedral, one with developed faces is subhedral, one with undeveloped crystal faces is called anhedral. The long axis of a euhedral quartz crystal has a six-sided prismatic habit with parallel opposite faces. Aggregates can be formed of individual crystals with euhedral to anhedral grains; the arrangement of crystals within the aggregate can be characteristic of certain minerals. For example, minerals used for asbestos insulation grow in a fibrous habit, a mass of fine fibers; the terms used by mineralogists to report crystal habits describe the typical appearance of an ideal mineral. Recognizing the habit can aid in identification as some habits are characteristic.
Most minerals, however, do not display ideal habits due to conditions during crystallization. Euhedral crystals formed in uncrowded conditions with no adjacent crystal grains are not common. Factors influencing habit include: a combination of two or more crystal forms. Minerals belonging to the same crystal system do not exhibit the same habit; some habits of a mineral are unique to its variety and locality: For example, while most sapphires form elongate barrel-shaped crystals, those found in Montana form stout tabular crystals. Ordinarily, the latter habit is seen only in ruby. Sapphire and ruby are both varieties of the same mineral: corundum; some minerals may replace other existing minerals while preserving the original's habit: this process is called pseudomorphous replacement. A classic example is tiger's eye quartz, crocidolite asbestos replaced by silica. While quartz forms prismatic crystals, in tiger's eye the original fibrous habit of crocidolite is preserved; the names of crystal habits are derived from: Predominant crystal faces.
Crystal forms. Aggregation of crystals or aggregates. Crystal appearance. Abnormal grain growth Grain growth
Carbonate minerals are those minerals containing the carbonate ion, CO32−. Calcite group: trigonal Calcite CaCO3 Gaspeite CO3 Magnesite MgCO3 Otavite CdCO3 Rhodochrosite MnCO3 Siderite FeCO3 Smithsonite ZnCO3 Spherocobaltite CoCO3 Aragonite group: orthorhombic Aragonite CaCO3 Cerussite PbCO3 Strontianite SrCO3 Witherite BaCO3 Rutherfordine UO2CO3 Natrite Na2CO3 Dolomite group: trigonal Ankerite CaFe2 Dolomite CaMg2 Huntite Mg3Ca4 Minrecordite CaZn2 Barytocite BaCa2 Carbonate with hydroxide: monoclinic Azurite Cu322 Hydrocerussite Pb322 Malachite Cu2CO32 Rosasite 2CO32 Phosgenite Pb2Cl2 Hydrozincite Zn526 Aurichalcite 526 Hydromagnesite Mg542.4H2O Ikaite CaCO3·6 Lansfordite MgCO3·5 Monohydrocalcite CaCO3·H2O Natron Na2CO3·10 Zellerite Ca2·5The carbonate class in both the Dana and the Strunz classification systems include the nitrates. IMA-CNMNC proposes a new hierarchical scheme; this list uses the classification of Nickel–Strunz. Abbreviations: "*" – discredited. "?" – questionable/doubtful.
"REE" – Rare-earth element "PGE" – Platinum-group element 03. C Aluminofluorides, 06 Borates, 08 Vanadates, 09 Silicates: Neso: insular Soro: grouping Cyclo: ring Ino: chain Phyllo: sheet Tekto: three-dimensional framework Nickel–Strunz code scheme: NN. XY.##x NN: Nickel–Strunz mineral class number X: Nickel–Strunz mineral division letter Y: Nickel–Strunz mineral family letter ##x: Nickel–Strunz mineral/group number, x add-on letter 05. A Carbonates without additional anions, without H2O 05. AA Alkali carbonates: 05 Zabuyelite. AB Alkali-earth carbonates: 05 Calcite, 05 Gaspeite, 05 Magnesite, 05 Rhodochrosite, 05 Otavite, 05 Spherocobaltite, 05 Siderite, 05 Smithsonite. AC Alkali and alkali-earth carbonates: 05 Eitelite, 10 Nyerereite, 10 Natrofairchildite, 10 Zemkorite. AD With rare-earth elements: 05 Sahamalite-. B Carbonates with additional anions, without H2O 05. BA With Cu, Co, Ni, Zn, Mg, Mn: 05 Azurite, 10 Chukanovite, 10 Malachite, 10 Georgeite, 10 Pokrovskite, 10 Nullaginite, 10 Glaukosphaerite, 10 Mcguinnessite, 10 Kolwezite, 10 Rosasite, 10 Zincrosasite.
BB With alkalies, etc.: 05 Barentsite, 10 Dawsonite, 15 Tunisite, 20 Sabinaite 05. BC With alkali-earth cations: 05 Brenkite, 10 Rouvilleite, 15 Podlesnoite 05. BD With rare-earth elements: 05 Cordylite-, 05 Lukechangite-. BE With Pb, Bi: 05 Shannonite, 10 Hydrocerussite, 15 Plumbonacrite, 20 Phosgenite, 25 Bismutite, 30 Kettnerite, 35 Beyerite 05. BF With, SO4, PO4, TeO3: 05 Northupite, 05 Ferrotychite, 05 Manganotychite, 05 Tychite. C Carbonates without additional anions, with H2O 05. CA With medium-sized cations: 05 Nesquehonite, 10 Lansfordite, 15 Barringtonite, 20 Hellyerite 05. CB With large cations: 05 Thermonatrite, 10 Natron, 15 Trona, 20 Monohydrocalcite, 25 Ikaite, 30 Pirssonite, 35 Gaylussite, 40 Chalconatronite, 45 Baylissite, 50 Tuliokite 05. CC With rare-earth elements: 05 Donnayite-, 05 Mckelveyite-*, 05 Mckelveyite-, 05 Weloganite. D Carbonates with additional anions, with H2O 05. DA With medium-sized cations: 05 Dypingite, 05 Giorgiosite, 05 Hydromagnesite, 05 Widgiemoolthalite.
DB With large and medium-sized cations: 05 Alumohydrocalcite, 05 Para-alumohydrocalcite, 05 Nasledovite.
A pegmatite is an igneous rock, formed underground, with interlocking crystals larger than 2.5 cm in size. Most pegmatites are found in sheets of rock near large masses of igneous rocks called batholiths; the word pegmatite derives from Homeric Greek, πήγνυμι, which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite. Most pegmatites are composed of quartz and mica, having a similar silicic composition as granite. Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene and other unusual minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions. Crystal size is the most striking feature of pegmatites, with crystals over 5 cm in size. Individual crystals over 10 metres long have been found, many of the world's largest crystals were found within pegmatites; these include spodumene, microcline and tourmaline. Crystal texture and form within pegmatitic rock may be taken to extreme size and perfection.
Feldspar within a pegmatite may display exaggerated and perfect twinning, exsolution lamellae, when affected by hydrous crystallization, macroscale graphic texture is known, with feldspar and quartz intergrown. Perthite feldspar within a pegmatite shows gigantic perthitic texture visible to the naked eye; the product of pegmatite decomposition is euclase. The single feature, diagnostic to all pegmatites is their large size crystal components. Pegmatite bodies are of minor size compared to typical intrusive rock bodies. Pegmatite body size is on the order of magnitude of one to a few hundred meters. Compared to typical igneous rocks they are rather inhomogeneous and may show zones with different mineral assemblages. Crystal size and mineral assemblages are oriented parallel to the wall rock or concentric for pegmatite lenses; the number of crystal nuclei in pegmatites must be low and the ability of the necessary chemical components needed for crystal growth to migrate to the crystal surfaces must be enhanced to allow gigantic crystals to grow in pegmatites.
Thus, the possible growth mechanisms in a wide variety of known pegmatites may involve a combination of the following processes. The mineralogy of a pegmatite is in most cases dominated by some form of feldspar with mica and with quartz, being altogether "granitic" in character. Beyond that, pegmatite may include most minerals associated with granite and granite-associated hydrothermal systems, granite-associated mineralisation styles, for example greisens, somewhat with skarn associated mineralisation, it is however impossible to quantify the mineralogy of pegmatite in simple terms because of their varied mineralogy and difficulty in estimating the modal abundance of mineral species which are of only a trace amount. This is because of the difficulty in counting and sampling mineral grains in a rock which may have crystals from centimeters to meters across. Garnet almandine or spessartine, is a common mineral within pegmatites intruding mafic and carbonate-bearing sequences. Pegmatites associated with granitic domes within the Archaean Yilgarn Craton intruding ultramafic and mafic rocks contain red and brown almandine garnet.
Tantalum and niobium minerals are found in association with spodumene, tourmaline, cassiterite in the massive Greenbushes Pegmatite in the Yilgarn Craton of Western Australia, considered a typical metamorphic pegmatite unassociated with granite. Syenite pegmatites contain large feldspathoid crystals instead. Pegmatite is difficult to sample representatively due to the large size of the constituent mineral crystals. Bulk samples of some 50–60 kg of rock must be crushed to obtain a meaningful and repeatable result. Hence, pegmatite is characterised by sampling the individual minerals that compose the pegmatite, comparisons are made according to mineral chemistry. Geochemically, pegmatites have major element compositions approximating "granite", when found in association with granitic plutons it is that a pegmatite dike will have a different trace element composition with greater enrichment in large-ion lithophile elements, beryllium, aluminium and lithium, thorium, cesium, et cetera. Enrichment in the unusual trace elements will result in crystallisation of unusual and rare minerals such as beryl, columbite, zinnwaldite and so forth.
In most cases, there is no particular genetic significance to the presence of rare mineralogy within a pegmatite, however it is possible to see some causative and genetic links between, tourmaline-bearing granite dikes and tourmaline-bearing